Referring to FIG. 10, a conventional blowtorch 90 includes a reservoir 96 and a valve. The valve includes a housing 91 and a plunger 94. The housing 91 includes a chamber 97, an inlet 92 and an outlet 93. The chamber 97 includes a conical portion through which the inlet 92 is communicated with the outlet 93. The plunger 94 is installed in the chamber 97 in a movable manner. The plunger 94 includes a conical portion for insertion into the conical portion of the chamber 97. The flow rate of gas is determined by the position of the conical portion of the plunger 94 relative to the conical portion of the chamber 97. It is intended that the communication between the inlet 92 and the outlet 93 be interrupted by the conical portion of the plunger 94 when the conical portion of plunger 94 is completely inserted in the conical portion of the chamber 97. To this end, the conical portion of the plunger 94 must be shaped in perfect compliance with the conical portion of the chamber 97. This is, however, difficult in reality. In case the conical portion of the plunger 94 is not shaped in perfect compliance with the conical portion of the chamber 97, the flow of the gas cannot be completely shut off, and this is dangerous.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in the prior art.